Flowering phenology of a widespread perennial herb shows contrasting responses to global warming between humid and non-humid regions

Plant phenology was assessed as one of the most key Essential Biodiversity Variables on species functional traits, which underpins a variety of aspects of ecosystem function and is a vital determinant of species distribution. Flowering phenology is one of the most sensitive indicators of the effects of recent climatic change. Understanding of intraspecific variation in phenological responses to climate change can contribute to the accurate prediction of phenology and the assessment of potential impacts of climate change on organisms. However, this intraspecific variation in phenological sensitivity in natural systems is still unclear, especially at large spatial scales. Using the widespread perennial herbSpiranthes sinensis, we quantified intraspecific variation in phenological responses to warming among groups located along climatic gradients. Phenological data were derived from 1,681 collections of herbarium specimens and photographs across eastern Asia and southeastern Australia over the period 1902-2017 and spans eight humid and eight non-humid regions. We found that peak flowering dates ofSpiranthe sinensis(FLss) showed substantial intraspecific variation in temperature sensitivity, ranging from -5.16 +/- 1.13 to 4.16 +/- 0.90 days/degrees C. Across all 16 regions, FLss exhibited the strongest delayed response to warming in southeastern Australia. Temperature sensitivity of the FLss was significantly correlated with annual precipitation and aridity index of a region, suggesting a possible role of declined water availability in reducing temperature sensitivity. Notably, contrasting phenological responses to warming were found between collections with different humidity regimes: humid regions generally flowered earlier (M: -3.57 days/degrees C) and non-humid regions exhibited slightly delayed flowering (M: 1.25 days/degrees C). These findings provide empirical evidence of substantial intraspecific variation in phenological sensitivity across large spatial scales, and highlights that soil water availability may play a key role in a warming planet, especially in non-humid regions.